Optical illusion

[cpgos]

The attached files show a standard industrial enclosure with a front and rear perforated door. The perforations are hexagons ~5mm wide and ~10mm apart and the enclosure itself is about 1m from front to back. The photographs were taken from a distance of ~20m.

When viewed from this distance there seems to be some kind of magnification that makes the holes in the rear much larger than they actually are. Could somebody please suggest an explanation for what may be the cause of this apparant magnification?

Could it have something to do with diffraction?

Best regards,
cpgos

[hubie]

What you are seeing is a nice example of a Moire pattern (by the way, how does one add accented characters in this editor?). A great example of this effect, for parallel lines, is shown at the Mathworks site (http://mathworld.wolfram.com/MoirePattern.html).

The obligatory Wikipedia link is here (http://en.wikipedia.org/wiki/Moir%C3%A9_pattern).

[cpgos]

Thank you for your response and for the very informative weblinks.

This is an effect that I have also often seen when driving under bridges that have vertical railings. The railings on either side are slightly offset relative to ones current position.

On my keyboard I get accented characters like ~ simply by holding down shift and pressing the # key.

Best regards,
cpgos